1. Field of the Invention
The present invention relates generally to an optical head recording and/or reproducing information on or from an optical or magneto-optical disc (disk) using optical or magneto-optical characteristics, and more particularly, to an optical head having an innovatively reduced thickness.
2. Description of the Related Art
In general, optical heads are used to record and/or reproduce information on or from compact discs (CDs), digital versatile discs (DVDs), blue-ray discs (BDs), or MP3 players using optical discs. An optical head includes many individual optical parts such as the light transmitting/receiving elements (i.e., the light emitting/receiving elements including a laser diode (LD) and a photo diode (PD)), a mirror, a prism, a beam splitter (BS), a polarization beam splitter (PBS), and a hologram optical element (HOE).
An optical head is made by assembling these individual optical parts each of which has thickness and volume in the 3-dimensional space, and this is an obstacle to reducing the overall thickness of the optical head. However, reduction of the optical head thickness is an important design requirement of the modern mobile optical discs, which are no longer stationary but are portable devices, i.e., easily carryable and movable. To achieve this, the thickness of the optical head must be innovatively reduced.
FIG. 1 is a cross-sectional view of an example of an optical head used in an MP3 player according to prior art.
The optical head shown in FIG. 1 is published in PCT International Application No. PCT/US02/00875 and PCT International Publication No. WO 02/058059 A2, entitled “Beamshaper for Optical Head” by Dataplay, INC. In the optical head shown in FIG. 1, an LD 4, a PD 6, an objective lens 8, a prism 10, a mirror 12, and a PBS 14 are disposed 3-dimensionally on a substrate 2. As shown in FIG. 1, the beam 20 emitted from the LD 4 is incident on a disc 16 through the prism 10, the mirror 12, the PBS 14, and the objective lens 8. The beam 20 is reflected from the disc 16 and then incident on the PD 6 through the PBS 14.
Because each of the optical parts in the optical head as shown in FIG. 1 has a predetermined volume and disposed in the 3-dimensional space, the overall thickness of the optical head, even if the objective lens 8 is excluded, ends up being undesirably large for mobility. This also means that the overall thickness of an optical head such as that shown in FIG. 1 may not be readily reduced as long as many individual parts as shown in FIG. 1 are assembled into an optical head, mainly because the thickness of each of the individual parts will add up.
FIG. 2 is a cross-sectional view of another prior art example of an optical head for a BD using a blue laser beam manufactured by Sony Corporation.
The optical head shown in FIG. 2 is published in February 2003, entitled “Small Integrated Optical Head Device Using a Blue-violet Laser Diode for Blue-ray Disc System,” Jpn. J. Appl. Phys. Vol. 42(2003), pp. 880-884, Part 1. No. 2B.
The optical head shown in FIG. 2 includes optical parts such as a blue beam LD 30, a 45 degree mirror 32, a half wave plate (HWP) 34, a grating 36, a PBS 38, a mirror 40, a HOE 42, a cylinder lens 44, a prism 46, a molded optical element, a PD IC 50, and a package 54 molded by a lead frame 52.
As shown in FIG. 2, the beam 56 emitted from the blue beam LD 30 is incident on a disc through the 45 degree mirror 32, the HWP 34, the grating 36, and the PBS 38. The beam 56 is reflected from the disc and then incident on the PD IC 50 through the PBS 38, the mirror 40, the HOE 42, and the cylinder lens 44.
The optical parts in the optical head shown in FIG. 2 are also disposed in a 3-dimensional space. In the optical head shown in FIG. 2, the HOE 42 is used; however, the overall thickness of the optical head still cannot be sufficiently and greatly reduced because the individual parts each occupying a predetermined volume in the 3-dimensional space are still used to assemble the optical head shown in FIG. 2.
As described above, the optical parts in a conventional optical head are disposed in a 3-dimensional space. This limits effective reduction of the overall thickness of a conventional optical head. As a result, the undesirable thickness of the conventional optical heads presents a fundamental obstacle to putting them together in an easily carryable, mobile optical disc for its intended practical portable use.